I can't speak for the author but I've experienced this issue a few times, with increasing frequency of late, on Firefox and even other apps (not Chrome). Especially if I'm browsing under private mode (which I often am, just because I don't like any cookies/cache to be saved for random sites). Now, it's not like it's some random site who's Javascript broke or something, perfectly functioning sites would stop working and display that CloudFlare access denied message, when they previously worked just fine.

The other app I'd experience issues with is Tachiyomi, a manga reader and scraper. Whilst it works fine for the most part, every once in a while I'd get blocked by CloudFlare, which prevents Tachiyomi from searching/accessing various manga sites. But if I access the said site via Chrome, it'd work just fine.

It's not just CloudFlare. Sometimes, when again browsing via Firefox's private mode and say I needed to run a Google search, Google sometimes throws a captcha at me because it finds my activities "suspicious".

Just so you know, there's nothing unusual about my internet setup - I'm just a standard home user, with a static-ish IP from a well known ISP. My public IP has been the same for over an year now, and I don't run any web/mail servers or anything that my ISP or a website would dislike.

What it is, is just plain discrimination. Just because I have my privacy filters up and blocking all tracking and crap, it's seeing me as suspicious. If this sort of stuff is going to be the norm, I can only imagine how much more bleak our future would be if Google's WEI went into effect.

It's popular because many people don't have static IP, behind a CGNAT, or simply don't want their residential IP address exposed, so their option is either use a vps as a tunnel (cost money) or use cloudlare tunnel (free). Obviously the free one get more use.

Who would you recommend as an alternative DNS provider?

Someone I know who works in payments told me they had to go to CF because of the insane amount of DDoS attacks they were facing.

While having three ISPs and mitigating a boatload of DDoS on their own infrastructure they were simply unable to cope with the persistence.

They first tried another provider, but they handled less DDoS than their own internal systems.

Cloudflare wasn’t even sure they wanted them as a customer.

Some of the biggest attacks mitigated by Cloudflare last year (they wrote about it) was this client.

The author explicitly says that they didn't tamper with headers or user agent. I'm neutral/not knowledgeable on the rest of your comment, but wanted to clarify that point.

The problem is that they're a monopoly abusing their position to make it impossible to have the basic privacy you should be unconditionally entitled to to browse the internet.

It should be blanket illegal to block/discriminate against traffic based on the browser used in literally all contexts.

How can you like cloud flare despite this?

You're wrong to like cloudflare. Thats why.